Power normalization of angular information from three-wire synchro source

ABSTRACT

An angle defining synchro output signal is subject to variation stemming from synchro induced phase shift and transformation ratio variations between units, as well as by variations in carrier excitation source amplitude. By converting a three-wire synchro output to respective carrier signals modulated by sine and cosine functions of the synchro signal information angle, demodulating each synchronously with respect to a signal phased in accordance with one of the sine and cosine modulated signals, and subsequently dividing the demodulator outputs, an output signal proportional to the ratio of the sine and cosine functions of the angle is obtained which is not affected by changes in synchro phase shift, transformation ratio, and carrier energization magnitude.

Inventor James 11. McCollum, Jr.

' Cedar Rapids, Iowa Appl. No. 31,895

Filed Apr. 27, 1970 Patented Aug. 17, 1971 Assignee Collins RadioCompany Cedar Rapids, Iowa POWER NORMALIZATION OF ANGULAR INFORMATIONFROM THREE-WIRE SYNCHRO SOURCE References Cited UNITED STATES PATENTS2,580,148 12/1951 Wirkler 329/146 X 3,050,728 8/1962 Worley..... 328/133X 3,265,904 8/1966 Spencer 328/133 X Primary Examiner-Alfred L. BrodyAttorneys-Richard W. Anderson and Robert J. Crawford ABSTRACT: An angledefining synchro output signal is subject to variation stemming fromsynchro induced phase shift and transformation ratio variations betweenunits, as well as by variations in carrier excitation source amplitude.By converting a three-wire synchro output to respective carrier 7 Claims1 Drawing signals modulated by sine and cosine functions of the synchroU.S. Cl 329/50, signal information angle, demodulating eachsynchronously 318/654, 325/476, 328/133, 328/155, 329/135, with respectto a signal phased in accordance with one of the 329/146 sine and cosinemodulated signals, and subsequently dividing Int. Cl. 03d 3/18 thedemodulator outputs, an output signal proportional to the Field ofSearch 329/135, ratio of the sine and cosine functions of the angle isobtained 137, 50, 146; 328/133, 155; 325/476; 318/654, which is notaffected by changes in synchro phase shift, trans- 655, 633 formationratio, and carrier energization magnitude.

0 l3 r19 X MAX SIN SYNCHRONOUS E sm d1 3 WIRE 400HZ DEMODULATOR 25 DC 2714 Y TO 2 4 TAN Q DEMODULATOR 22 11 \lZ AND REFERENCE l COCNOVSIRNTEERDRIVER 23 28 I SYNCH iouous MAX cos 9 E MAX 08 Q o c POWER NORMALIZATIONOF ANGULAR INFORMATION FROM THREE-WIRE SYNCHRO SOURCE This inventionrelates generally to the derivation of angular information from athree-wire synchro signal source and more particularly to thedevelopment of angular information output signal from such a three-wiresource by a means which eliminates errors due to applied voltages, phaseshift, and transformation ratios. The synchro is a well-known deviceproviding three-wire output information the relative amplitudes andphase relationships of which are definitive of the angular orientationof the synchro rotor winding with respect to a three-phase statorwinding. The present invention relates particularly to applications ofthree-wire synchros utilized to provide position information to controlsystem and wherein it is desirable to eliminate variations in gain dueto variations in synchro excitation voltage, variations intransformation ratios between various synchro units which might beemployed in a given circuitry, and variations due to phase shift throughthe synchro.

The object of the present invention is accordingly the provision'of acircuitry to develop an output signal which is a function of three-wiresynchro input angular information signal and to develop the signal insuch a manner as to eliminate signal variations due to power changes,transformation ratio changes and phase shifts.

The presentinvention is featured in provision of means for convertingthe three-wire synchro information to respective sine and cosineinformation signals and utilizing one of the sine and cosine informationsignals as a reference driving source for synchronous demodulationprocesses performed on the quadrature signals for elimination of errorsdue to phase shift. The synchronously demodulated quadrature signals aresubsequently divided to provide an output signal proportional to thetangent of the input angular information, i.e. tangent Q, the dividingprocess eliminating the variations attributed to a function of synchroexcitation voltage per se and the transformation ratio of the synchro.

These and other features and objects of the present invention willbecome apparent upon reading the following description'with reference tothe drawing in which the single FIGURE is a functional diagram of apower normalization circuitry for a three-wire synchro source inaccordance with the present invention.

Numerous implementations are known in the art wherein three-wire synchrosignals are converted to a single (two-wire) output proportional to theinformation angle per se or a given trigonometric function of theinformation angle defined collectively by the amplitudes and phases ofthe three-wire synchro output signal. in systems where the outputinformation angle, or a function of this angle, must be extremelyaccurate, errors due to variations in the synchro excitation voltage,transformation ratios between various synchro units which might beemployed, and phase shift through the synchro may be intolerable. Thepresent invention extracts an output information signal in the form oftrigonometric function of the angle collectively defined by thethree-wire synchro input signal which is immune to thesesources oferror.

With reference to FIG. 1, a synchro comprising a rotor 11 andthree-phase stator winding 12 develops outputs 13, 14, and 15, thecomparative instantaneous amplitudes and phase relationships of whichcollectively define the angular relationship 1 between the rotor 11 ofthe synchro and the stator winding 12. A source of 26-volt 400-l-lz.cycle excitation (carrier) signal might be applied to the rotor 11. Forthe purpose of the present invention the three-wire output information13 14-15 is applied to a three-wire to sine and cosine convertercircuitry 16. The converter 16 might comprise, for example, a Scott-Ttransformer which receives a three-wire synchro signal and converts thesignal to first and second outputs l7 and 18 respectively proportionalto the sine and cosine of the angle D. Thus in FIG. 1 the output 17 fromthe converter 16 is designated E sin 4 while the'output 18 from theconverter 16 is designated E cos 1 'Outputs l7 and 18 would comprise400-Hz. carrier signals amplitude modulated in proportion to sine 9 andcosine 1 respectively.

Output signals 17 and 18 from converter 16 thus comprise two signalswhich are proportional to the applied power (E,,,,,,) and the angularposition of the synchro 1 These two outputs are applied to separatesynchronous demodulators 19 0 and 20 which convert the 400-l-lz.amplitude modulated carrier signals to DC signals. The conversion orsynchronous demodulation to DC signals is made with respect to the 400-1-12. reference frequency by generating a demodulator reference signalfrom the output signal 18 from converter 16 which is amplitude modulatedin accordance with cosine 4 Accordingly output 18, proportional to Ecosine d is applied as an input to synchronous demodulator 20 and alsoas an input to a demodulator reference driver 21.

The reference driver 21 might comprise any one of a number ofoperational amplifier implementations which converts the applied signalto a square wave output signal which switches at the zero crossings ofthe 400-Hz. carrier applied. The output from the reference driver 21 isaccordingly a square wave signal the phase of which is precisely definedby the 4QO-Hz. carrier signal. This reference process (as opposed to useof the carrier source per se for reference) eliminates errors due tophase shift between the 400-Hz. input to the synchro 10 and the 400-112.output signal from the synchro.

The synchronous demodulators l9 and 20 might be any one of a number ofsynchronous implementations which function as a suppressed carrierdemodulators and provide a DC output proportional to the amplitude ofthe modulated input signal with the polarity of the output being afunction of the phase relationship of the input signal and the injectedcarrier signal. In the present instance, the latter signal is the output22 from the demodulator reference driver circuit 21.

The outputs from the two synchronous demodulators 19 and 20 (E sine Dand E cosine 1 respectively) are applied as respective inputs 25 and 26to a divider circuitry 27, the function of which is to perform thecomputation E sine 1 /E,,,,,, cosine 1 tangent D.

The division process performed by divider 27 eliminates the E referenceinformation and leaves only the angular position information in the formof the tangent of the angle 4 By eliminating the E reference (which is afunction of the synchro excitation voltage and the transformation ratioof the synchro) variations due to these two parameters are eliminated,leaving only angular position information.

Obvious limitations-to the above defined technique exist due to thenature of the tangent function. in a typical utilization, the operationof this system might normally be restricted to angles of (0:45) or(180145) degrees. This range, however, is more than adequate for manyapplications, for example, the use of such a circuit in an aircraftguidance roll angle reference signal development in a system where theaircraft is normally never commanded to a roll attitude greater than Forthis reason the demodulator reference driver utilizes the E cosineoutput 18 from the converter 16 since, over the range of operation, thecosine function of l does not change sign and the modulated carriersignal proportional to E, cosine I (output 18 from converter 16) doesnot change phase or go through zero between values of 1 between :90".Obviously should the sine D proportional signal 17 from converter 16 beutilized as the demodulator reference driver input, there would be noreference drive signal for values of D=0 (or since the since function iszero and the magnitude of the output 17 from converter 16 would be atthese values of 1 Operation about 90 or 270 results in a sine func tionwhich is not zero, but the tangent function would be discontinuous atthese points.

Over the range of operation in a typical system such as, for example, 45to +45 about 0 the output 25 from synchronous demodulator 19 whichreceives the sine proportional input signal is of positive polaritybetween the values of q between and +45 and of negative polarity due toa phase reversal in the 400-Hz. carrier signal carrying the sinusoidalmodulation for values of 1 between 0 and 45.

Thus, the outputs 25 and 26 from the respective synchronousdemodulators, when divided in divider 27 develop an output 28proportional to tangent 1 the sign of which is positive for values of 1greater than 0 and is negative for values of I less than 0. The output28 is thus a true analog output as concerns the tangent function of theangle 1 defined by the three-wire synchro input. The output 28 is devoidof errors which might normally be introduced due to variations inapplied synchro excitation voltage, phase shift within the synchro andvariation in transformation ratios between different synchros employedin a given implementation.

Although the present invention has been defined with respect to aparticular embodiment thereof, it is not to be so limited as changesmight be made therein which fall within the scope of the invention asdefined by the appended claims.

Iclaim:

1. Means for extracting angular output information from a synchroangular information signal, comprising signal conversion means receivingsaid synchro signal as an input thereto and developing first and secondoutput signals respectively proportional to the sine and cosine functionof the angular information defined by said synchro signal, said synchrosignal and the outputs from said conversion means comprising carriersignals the amplitude modulation and carrier phases of which define saidangular information, a first synchronous demodulator means receivingsaid first converter output signal as a first input thereto, a secondsynchronous demodulator receiving said second converter output signal asa first input thereto, a demodulator reference driver circuitryreceiving said second converter output signal and developing an outputwith phase corresponding to one said converter output signals means forapplying the outputs from said demodulator reference driver circuitry asrespective second inputs to each of said first and second synchronousdemodulators, said synchronous demodulators being adapted to provide adirect current voltage output signal the magnitude of which isproportional to the modulation component of the first input thereto andthe polarity of which is a function of the phase relationship betweencarrier component of the first input thereto and the output from saiddemodulator reference driver circuitry, signal dividing means, means forapplying the outputs from said first and second synchronous demodulatorsas respective inputs to said signal dividing means, the output from saiddividing means being proportional to the quotient of the output fromsaid first synchronous demodulator divided by the output from saidsecond synchronous demodulator whereas the output from said dividingmeans is proportional to the tangent of the angular information angledefined by said synchro input signal and is substantially unaffected byvariations in amplitude of the energizing carrier signal source, byvariations between transformation ratios of difierent ones of saidsynchro input sources which might be connected in circuit therewith, andby phase shift in said synchro.

2. Means for converting a three-wire synchro input signal comprised offirst, second, and third signal lines, the relative signal amplitudesbetween pairs of said lines and phases of voltage induced in said linesbeing collectively definitive of an information angle 1 means forconverting said three-wire angular information input signal to first andsecond angular information signals respectively proportional to the'sineand cosine functions of said information angle D, means for demodulatingeach of said first and second last defined signals against a phasereference based on the phase of said signal proportional to cosine Iwherein first and second direct current voltage signals the amplitudesof which are respectively proportional to sine and cosine of theinformation angle I are developed, and means for dividing said lastnamed sine proportional signal with said last named cosine proportionalsignal to develop an output signal the magnitude of which isproportional to the tangent of said angular information signal I saidoutput signal being unaffected by variations in synchro transformationratios, by variations in the magnitude of the energizing carrier signalsource for said synchro signal, and by phase shift in said synchro.

3. Means as defined in claim 1 wherein said information angle 3 equals:mH-O and inn-0, where n is an integer including the integer zero and 0is less than 90.

4. Means as defined in claim 2 wherein said information angle D equalstnn+0 and inn-0, where n is an integer in cluding the integer zero and 0is less than 90.

5. Means as defined in claim 1 wherein the angle defined by said synchroinput signal varies between 0 or 180 plus or minus a predefined angle 0,where 0 is greater than 0 and less than 90.

6. Means as defined in claim 2 wherein the angle defined by said synchroinput signal varies between 0 or 180 plus or minus a predefined angle 0,where 0 is greater than 0 and less than 90.

7. Means for converting a three-wire synchro input signal comprised offirst, second, and third signal lines, the relative signal amplitudesbetween pairs of said lines and phases of voltage induced in said linesbeing collectively definitive of an information angle 1 means forconverting said three-wire angular information input signal to first andsecond angular information signals respectively proportional to the sineand cosine functions of said information angle 1 means for demodulatingeach of said first and second last defined signals against a phasereference based on the phase of at least one of said signalsproportional to sine P and cosine I wherein first and second directcurrent voltage signals the amplitudes of which are respectivelyproportional to sine and cosine of the information angle 1 aredeveloped, and means for deriving the ratio of said last named signalsto develop an output signal the magnitude of which is proportional to anangular function of said angular information signal I said output signalbeing unaffected by variations in synchro transformation ratios, byvariations in the magnitude of the energizing carrier signal source forsaid synchro signal, and by phase shift in said synchro.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,694Dated August 17 1971 Inventor(s) James Mccollum, r

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 7, after "of" insert an line 16, after "to" insert a line24, after "of" insert a Column 2, line 68, "since" should read sine line69, aftel "be" insert zero Signed and sealed this 27th day of June 1972.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents ORM P Q-1050410439 USCOMM-DC GO376-P69 9 U S. GOVERNMENTPRINTING OFFICE I 1969 0-356-33b

1. Means for extracting angular output information from a synchroangular information signal, comprising signal conversion means receivingsaid synchro signal as an input thereto and developing first and secondoutput signals respectively proportional to the sine and cosine functionof the angular information defined by said synchro signal, said synchrosignal and the outputs from said conversion means comprising carriersignals the amplitude modulation and carrier phases of which define saidangular information, a first synchronous demodulator means receivingsaid first converter output signal as a first input thereto, a secondsyncHronous demodulator receiving said second converter output signal asa first input thereto, a demodulator reference driver circuitryreceiving said second converter output signal and developing an outputwith phase corresponding to one said converter output signals, means forapplying the outputs from said demodulator reference driver circuitry asrespective second inputs to each of said first and second synchronousdemodulators, said synchronous demodulators being adapted to provide adirect current voltage output signal the magnitude of which isproportional to the modulation component of the first input thereto andthe polarity of which is a function of the phase relationship betweencarrier component of the first input thereto and the output from saiddemodulator reference driver circuitry, signal dividing means, means forapplying the outputs from said first and second synchronous demodulatorsas respective inputs to said signal dividing means, the output from saiddividing means being proportional to the quotient of the output fromsaid first synchronous demodulator divided by the output from saidsecond synchronous demodulator whereas the output from said dividingmeans is proportional to the tangent of the angular information angledefined by said synchro input signal and is substantially unaffected byvariations in amplitude of the energizing carrier signal source, byvariations between transformation ratios of different ones of saidsynchro input sources which might be connected in circuit therewith, andby phase shift in said synchro.
 2. Means for converting a three-wiresynchro input signal comprised of first, second, and third signal lines,the relative signal amplitudes between pairs of said lines and phases ofvoltage induced in said lines being collectively definitive of aninformation angle phi , means for converting said three-wire angularinformation input signal to first and second angular information signalsrespectively proportional to the sine and cosine functions of saidinformation angle phi , means for demodulating each of said first andsecond last defined signals against a phase reference based on the phaseof said signal proportional to cosine phi wherein first and seconddirect current voltage signals the amplitudes of which are respectivelyproportional to sine and cosine of the information angle phi aredeveloped, and means for dividing said last named sine proportionalsignal with said last named cosine proportional signal to develop anoutput signal the magnitude of which is proportional to the tangent ofsaid angular information signal phi , said output signal beingunaffected by variations in synchro transformation ratios, by variationsin the magnitude of the energizing carrier signal source for saidsynchro signal, and by phase shift in said synchro.
 3. Means as definedin claim 1 wherein said information angle phi equals + or - n pi + thetaand + or - n pi - theta , where n is an integer including the integerzero and theta is less than 90* .
 4. Means as defined in claim 2 whereinsaid information angle phi equals + or - n pi + theta and + or - n pi -theta , where n is an integer including the integer zero and theta isless than 90* .
 5. Means as defined in claim 1 wherein the angle definedby said synchro input signal varies between 0* or 180* plus or minus apredefined angle theta , where theta is greater than 0* and less than90* .
 6. Means as defined in claim 2 wherein the angle defined by saidsynchro input signal varies between 0* or 180* plus or minus apredefined angle theta , where theta is greater than 0* and less than90* .
 7. Means for converting a three-wire synchro input signalcomprised of first, second, and third signal lines, the relative signalamplitudes between pairs of said lines and phases of voltage induced insaid lines being collectively definiTive of an information angle phi ,means for converting said three-wire angular information input signal tofirst and second angular information signals respectively proportionalto the sine and cosine functions of said information angle phi , meansfor demodulating each of said first and second last defined signalsagainst a phase reference based on the phase of at least one of saidsignals proportional to sine phi and cosine phi wherein first and seconddirect current voltage signals the amplitudes of which are respectivelyproportional to sine and cosine of the information angle phi aredeveloped, and means for deriving the ratio of said last named signalsto develop an output signal the magnitude of which is proportional to anangular function of said angular information signal phi , said outputsignal being unaffected by variations in synchro transformation ratios,by variations in the magnitude of the energizing carrier signal sourcefor said synchro signal, and by phase shift in said synchro.